Hypoxia within regions of solid tumors is associated with resistance to standard treatments, particularly radiotherapy. The hypoxia occurs in part because the tumor's vasculature is highly unordered and leaves significant portions of the tumor unperfused. Conventional drug therapy, which depends on reaching the cancer through the bloodstream, can be less effective in hypoxic tumors.
Drug designers have taken advantage of the hypoxic regions in tumors and designed anticancer drugs that are specifically active or activated under hypoxic conditions. For example, hypoxia-activated prodrugs are chemically modified to be inactive, but when administered to the body and exposed to hypoxic conditions (such as in a tumor), they are metabolized or otherwise converted into the active, anticancer form. Despite these new drugs, there is an ongoing need for innovative approaches to anticancer therapy.